The invention relates generally to electronic digital watches and clocks, and more specifically concerns a method and apparatus for correcting errors in electronic digital timepieces.
In the past, electronic digital clocks or watches have provided no convenient method for the user to alter the clock rate to match a calibration source or signal. However, most clocks or watches do have, internally, a small adjustable trimmer capacitor that is used to "pull" the resonant frequency of a quartz crystal oscillator that operates, for example, at a frequency of 2.sup.15 Hertz.
The trimmer capacitor is usually initially adjusted so as to set the oscillator frequency equal to a standard. The accuracy can be set to seconds per week. But once set, such things as crystal aging, temperature variations, and wearing habits alter the clock rate. The clock rate is almost never adjustable from outside the clock or the watch. Furthermore, to set the oscillator to one second per week (about one part in 2.sup.19) requires setting the frequency to an equal accuracy. This is especially difficult because altering the clock case configuration by opening or closing it changes the influence of the case's stray capacitance on the oscillator frequency; in addition, this influence varies from watch to watch.
Of even greater importance is that the great majority of users lack sophisticated calibration equipment and are unable to easily or simply adjust the clock or watch rate even if the adjustment can be made externally. Most users have access only to time signals broadcast on local radio stations. The user must turn the trimmer adjustment through a small angle then wait a week or so to observe the effect. Based on the result, he then readjusts the trimmer and observes the result after another week; often, a third iterative adjustment is needed to arrive at an accuracy near one second per week.
It is the primary object of this invention to provide a method and apparatus for altering the clock rate of a timepiece to match a calibration source or signal.
Another object of this invention is to provide a timepiece in which the user, by means of external pushbutton controls, can easily and simply adjust the clock rate to a time standard.
A further object of this invention is to provide a method and apparatus for changing the clock rate of a timepiece without changing the frequency of the timepiece oscillator.
Still another object of this invention is to provide a method and apparatus for correcting the clock rate of a timepiece that does not require iterative adjustments to a reference frequency or rate.
Other objects and advantages of this invention will become apparent hereinafter in the specification and drawings.